In recent years, along with a growing interest in environmental issues, movement to try to utilize sunlight has become active. When utilizing sunlight, a mirror to reflect or condense sunlight is commonly used. Examples include a lighting mirror for shining sunlight on low-rise buildings on which sunlight is blocked by high-rise buildings, and a reflection mirror implemented in a light duct which is used to introduce sunlight into the interior of a building. The above mirrors are required to have functions such that they are light weight and unbreakable so that they are easy for treatment during delivery and installation, they can be made large and mass-produced in view of securing amount of lighting, they are flexible so that their shape can be agreed to shapes of installation places, and they are excellent in light-resistance and weather resistance in view of reflecting sunlight.
In general, as a commonly used mirror exhibiting high light reflectance, a glass mirror, in which a silver film is formed on one side of a transparent glass substrate by silver deposition, has been well known. However, since the glass mirror is apt to break to expose sharp edges, it always requires extreme caution in handling. Further, since the glass board with its thickness being extreme thin is hard to handle during the production process, it is required to have a certain degree of thickness. For this reason, in particular, for a large size product, the weight is significantly increased to require a special consideration during its delivery and installation.
For this reason, in consideration that there is danger of an injury due to breakage or difficulty in handling, it has been invented a mirror using a plastic resin board (for example, refer to Patent Document 1). The mirror described in Patent Document 1 is a plastic one in which a silver thin layer is formed on the surface of a transparent plastic resin in the form of plate or film. Since the substrate of the above plastic mirror is constituted of a plastic resin, it is possible for the plastic mirror to make it light weight and to reduce the production cost compared to a mirror whose substrate is constituted of a glass. Further, since the plastic resin is easy to be processed to a film shape, it is possible for the plastic resin to make it a highly flexible mirror.